CHAPTER VI 
Configuration of the ground at Santo Domingo—Excavation of valleys 
—Geology of the district—Decomposition of the rocks—Gold- 
mining—Auriferous quartz veins—Mode of occurrence of the gold 
—Lodes richer next the surface than at lower depths—Excavation 
and reduction of the ore—Extraction of the gold—‘‘ Mantos ”"— 
Origin of mineral veins—Their connection with intrusions of 
Plutonic rocks. 
THERE is scarcely any level land around Santo Domingo, but 
in every direction a succession of hills and valleys. The 
hills are not isolated; they run in irregular ranges, having 
mostly an east and west direction, but with many modifica- 
tions in their trend. From the main valleys numerous 
auxiliary ones cut deeply into the ranges, and bifurcate 
again and again, like the branches of a tree, forming channels 
for carrying off the great quantity of water that falls in these 
rainy forests. The branching valleys, all leading into main 
ones, and these into the rivers, have been excavated by sub- 
aérial agency, and almost entirely by the action of running 
water. It is the system that best effects the drainage of the 
country, and has been caused by that drainage. 
The wearing out of valleys near Santo Domingo proceeds 
more rapidly than in regions where less rain falls, and where 
the rocks are not so soft and decomposed. Even during the 
few years I was in Nicaragua there were some modifications 
of the surface effected; I saw the commencement of new 
valleys, and the widening and lengthening of others, caused 
not only by the gradual denudation of the surface, but by 
landslips, some of which occur every wet season. 
The rocks of the district are dolerytes, with bands and 
protrusions of hard greenstones. The decomposition of the 
dolerytes is very great, and extends from the tops of the hills 
to a depth (as proved in the mines), of at least two hundred 
feet. Next the surface they are often as soft as alluvial clay, 
and may be cut with a spade. This decomposition of the 
rocks near the surface prevails in many parts of tropical 
America, and is principally, if not always, confined to the 
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